Mopping up MRSA toxin with a sponge
Scientists have developed microscopic “nanosponges” that soak up a dangerous chemical released by the bacteria and prime the immune system.
In tests on mice, the nanosponge vaccine proved safe and effective, helping the animal’s immune systems block the harmful effects of MRSA toxin.
After just one injection of the tiny sponges, half the infected mice survived compared with just one in 10 of those treated with a conventional vaccine made from heat-treated bacterial toxin.
Two or more booster shots increased the survival rate to 100%.
Each tiny nanosponge measures just 85 nanometres across - small enough to fit 1,000 across the width of a human hair - and consists of a biodegradable polymer core wrapped in a covering of red blood cells.
The red corpuscles seize hold of toxin molecules and flag them up to the immune system. This triggers the production of antibodies that neutralise the toxin and prevent it wreaking havoc in the body.
“The nanosponge vaccine was … able to completely prevent the toxin’s damages in the skin, where MRSA infections frequently take place,” said Professor Liangfang Zhang, who led the US team from the University of California at San Diego.
MRSA, or methicillin-resistant Staphylococcus aureus, produces a “pore-forming” toxin called alpha-haemolysin that punches holes in cell membranes, causing the cells to leak to death.
The toxin is so powerful that, unaltered, it kills immune cells. Conventional vaccines that use the toxin have to weaken it through heat or chemical processing, but this also makes them less effective.
The nanosponges can use untreated toxin, which acts as a much more potent immunity trigger.
Unusually, the red blood cells coating the particles are unaffected by the toxin molecules. They simply lock them in place, so they remain visible to the immune system.
In a series of experiments many thousands of nanosponges were injected into infected mice. They proved effective at fighting the harmful effects of MRSA both in the bloodstream and on the skin.
The scientists believe tailored nanosponge vaccines could be developed to neutralise pore-forming toxins from a range of bacteria and other sources, such as snake venom.
It might even be possible to produce nanosponges capable of targeting a number of different toxins at once, they said.
The researchers wrote in the journal Nature Nanotechnology: “Here, we show a nanoparticle-based toxin-detainment strategy that safely delivers non-disrupted pore-forming toxins for immune processing.
“We anticipate that this study will open new possibilities in the preparation of anti-toxin vaccines against the many virulence factors that threaten public health.”
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